Sarcoidosis involving skeletal muscle: imaging findings and relative value of imaging procedures.

OBJECTIVE

Muscular involvement of sarcoidosis is rare and occurs in two forms: nodular and myopathic. In the nodular variety, patients have single or multiple nodules in the skeletal muscles. Patients with the myopathic type have myalgia, muscle weakness, and atrophy. The purpose of this study was to determine the imaging features of these two types of muscular sarcoidosis and to compare the merits of different imaging procedures in establishing the diagnosis.

MATERIALS AND METHODS

I retrospectivity reviewed the imaging findings of 28 patients with proved muscular sarcoidosis: 20 patients with the nodular type and eight with the myopathic type. Of the 20 patients with the nodular type, 20 had MR imaging, 17 had 67Ga scintigraphy, 10 had CT, six had sonography, and two had angiography. All eight patients with the myopathic type had MR imaging, and six of them had 67Ga scintigraphy.

RESULTS

In the nodular type of muscular sarcoidosis, the lesions were long and extended along muscle fibers. Axial MR images showed a star-shaped central structure of decreased signal intensity. Coronal and sagittal MR images showed three stripes, including an inner stripe of decreased signal intensity and outer stripes of increased signal intensity. After IV injection of gadopentetate dimeglumine, contrast-enhanced MR images showed enhancement in the peripheral area of the lesions of the nodular type. On sonograms, the central structure was hyperechoic and the peripheral area was hypoechoic relative to surrounding tissue. 67Ga scintigraphy showed increased uptake of radionuclide in the nodules. CT and angiography were of less diagnostic value. In the myopathic type, MR images showed no abnormalities. Myopathic involvement was visualized only with 67Ga scintigraphy, which showed diffusely increased uptake of radionuclide.

CONCLUSION

The unusual MR findings seen in the patients studied were suggestive of the nodular type of muscular sarcoidosis. 67Ga scintigraphy was useful for evaluating the whole body in patients with the nodular type and was the only imaging method that could show the myopathic type of involvement.